Centrex services may be provided to subscribers such as a business establishment having a main location connected to one local exchange and a remote or satellite location connected to another local exchange. In such centrex arrangements, incoming calls from outside the centrex business group come in via the main location exchange. Calls destined for the remote location are connected to a remote location station set via an interoffice trunk and the remote location exchange. A class of communication networks known as Integrated Services Digital Network (ISDN) provides subscribers with a variety of capabilities and control from the telephone station set used by the caller. ISDN centrex systems may be equipped with an attendant position from which call transfers, conferencing, etc., are controlled. ISDN station sets, also referred to as terminals, may be equipped with a "transfer" button and/or a "conference" button. Pressing these buttons during a call causes the terminal to transmit a message to the local exchange, which will bridge the attendant to the call connection to establish an audible connection with the attendant. When the party is at a remote location connected to one exchange and the attendant is at the main location connected to another exchange, the transfer/conference request must be transmitted from the one exchange to the other. In prior art analog systems customers may signal a transfer/conference request by momentary depression of the switchhook which is recognized at the local exchange as a flash. When a flash is received from a remote location in analog systems, it is transmitted to the main location exchange over an interoffice trunk equipped for analog flash signaling. In ISDN systems, communications between customer terminals and the exchange, occur by means of digitally encoded messages. Accordingly, when services of an attendant are needed, a digital message is sent to the local exchange. ISDN subscriber lines have B-channels and D-channels and all signaling messages such as "transfer" are transmitted via the D-channel. When the attendant is connected to another exchange, the ISDN message requesting attendant services must be transmitted to that exchange. A problem of prior art systems, however, is that there is no economical way to transmit the ISDN message to another exchange. Commonly available interoffice trunks are not equipped to accept and transmit ISDN messages and to provide a special interoffice trunk to handle such messages for this specific application is prohibitively expensive. Thus, in order to be able to provide communications from an ISDN terminal connected to one exchange to an attendant position connected to another exchange, another solution is desired.